Known coolant pumps and cooling fans often run directly off an engine shaft by means of a gear mechanism or a belt drive system, and therefore maintain a flow rate that is dependent only on the engine RPM. As a result, in such cases the coolant pump provides a coolant flow rate that is a function of the engine RPM and similarly the cooling fan maintains an airflow rate which also is a function of the engine RPM. Such traditional cooling systems have been designed on the premise of providing adequate cooling to the engine in the worst-case scenarios, i.e., a fully-loaded vehicle running at peak power engine speed and high ambient temperatures. However, these mechanically driven systems do not have the ability or the intelligence to alter their operating strategy and adjust to the actual cooling requirement of the engine in a variety of other operating situations. Thus, such known cooling systems do not provide optimum cooling to the engine at all times, but end up either under-cooling or over-cooling the engine during various on-the-road scenarios. This behavior reduces the engine efficiency, leading to higher fuel consumption and also adds auxiliary loads to the engine at times when the engine does not have any spare power.
Variable flow electric coolant pumps have recently been introduced. These electric coolant pumps respond to control signals to vary the rate at which coolant flows in the cooling circuit.